Eccentric grind on GTD boost pin - normal?

[regcheeseman]

I pulled the boost pin on my spare GTD engine to modify it before fitting to my tuned GTD in my daily caddy.

When I got it out it looked like this...


The working area is just about facing the camera and I noted that it was at about 50%....i.e rotating the boost pin could result in less or more boost enrichment.

Is this correct, can I just rotate the pin and re-fit it or should I grind it or should I do both!

[Vincent Waldon]

Yup, that's the design... you can change the boost response profile by rotating the pin and diaphragm before reassembly.

After you do this a few times you learn to put a dot on the diaphragm before disassembly so that you can remember where you started... in your case you can see where the pin has traced a line in the grease on the cone, so no problem.

[oldskool rich]

im confused, so when the pin is thinner more fuel goes in?

cant you grind it super thin? is there a limit? if you max fuel screw is too far in surly you wont get any or as much extra fuel on boost?

how do you set the spring to the right tension? do you just hav to play with it till it feels right?

[burn_your_money]

it's been a while since I read it but I think the FAQ explains how it works in the "make your 1.6td a faster car" or whatever it's called

[Vincent Waldon]

Like all tuning exercises the idea is the right amount of fuel with the right amount of air.

The beauty of this design is that it is automatically adding more fuel as you force in more air... perfect !

Sure you can grind the profile super thin... I suppose you could pull the pin out completely for max fuel, but if you go too far at any point on the profile you'll push past a reasonable mix and be into black smoke, higher EGTs, etc etc etc.

In the posted picture the OP looks like they had some room to rotate the plunger (move to a more aggressive part of the profile)... before going crazy with a grinder it might make sense to tweak and learn... watching EGT and boost at all times ?

[KTZed]

Ok I found this pic really interesting and rather than totally jacking this thread with a huge post I stole it and put it in my own thread about star wheel/boost pin/max fuel pictoral and questions. Feel free to post in that thread too if you have anything to add. Thanks regcheesman.

[jtanguay]

do a little searching  :wink:

http://vwdiesel.net/phpBB/viewtopic.php?t=4804&postdays=0&postorder=asc&highlight=wussy&start=15

[KTZed]

Hmm good thread there! One of those ones hidden under the guise of an unrelated subject line  :roll:

[jtanguay]

:lol:  i searched for hillfolk'r and wussy because i remember him calling it his wussy setting and seeing this boost pin that has a ton of material removed... and then the lotsa fuel setting  :twisted:

[regcheeseman]

From the 'witness' mark in my picture, it is obvoius that the pin can travel further as well.

There is a nylon spacer on my pin that limits it's travel - do you believe it is hitting this limit stop or merely travelling as far as the stock 7 psi will push it?

im confused, so when the pin is thinner more fuel goes in?

yep

cant you grind it super thin? is there a limit? if you max fuel screw is too far in surly you wont get any or as much extra fuel on boost?

I'm not gonna touch my 'max fuel screw - I don't like that approach but this pin is boost enricement pin so if you've turned your boost down or not playing leadfoot then you don't get the extra fuel.

You could grind it super thin but you'll start over fuelling and the EGT will get dangerous and the road behind turn to soot

how do you set the spring to the right tension? do you just hav to play with it till it feels right?

feg knows mate, I'm hoping it's right as stock, theres a star wheel inside the LDA that can load the spring with tension so room for improvement.

Mate with your engine spec, I thought you would have all this dialled.

[regcheeseman]

With the folowing annotated pic in mind I have the following issue...



Why do I need to rotate or grind the boost pin, surely at 7 psi the factory setting is correct, sure the correct procedure would be to allow the pin to travel further allong it's taper thus increasing the fuel at higher psi's but maintaining the original fuel curve?

Surely all the adjustability is there from factory without any grinding.

Also this max fuel screw - is this the same as the throttle stop or am I confused and does the LDA work above the max fuel settings or up to it's limit.

I have a spare NA pump i was gonna bin, but I've decided to strip it to understand how the pump works without wrecking my GTD one.

[regcheeseman]

With the folowing annotated pic in mind I have the following issue...



Why do I need to rotate or grind the boost pin, surely at 7 psi the factory setting is correct, sure the correct procedure would be to allow the pin to travel further allong it's taper thus increasing the fuel at higher psi's but maintaining the original fuel curve?

Surely all the adjustability is there from factory without any grinding.

Also this max fuel screw - is this the same as the throttle stop or am I confused and does the LDA work above the max fuel settings or up to it's limit.

I have a spare NA pump i was gonna bin, but I've decided to strip it to understand how the pump works without wrecking my GTD one.

Oh and the pic above show the nylon stop, should this be binned?

[Vincent Waldon]

The factory setting being "correct" is a matter of opinion as far as I'm concerned... it's "correct" in VW's eyes as they balance power, emissions, serviceability, reliability, how they've positioned the engine from a marketing perspective, etc etc etc.

"Correct" for you means deciding what you are solving for:  Power ?? Economy ??

I personally prefer tuning that is reversible... ie I can go back if what I do has an undesirable side effect.

Dialing back the star wheel inside the LDA that preloads the boost response spring will move the plunger's response curve down into the sections you've labeled "12 psi"... pushing in more fuel at lower boosts.

And it's reversible... don't like it, dial the spring back.

Rotating the plunger puts you on a more aggressive profile... and it's reversible.

Binning the nylon shim is reversible, but in my mind would be more about tuning for economy, since you are effectively lifting the plunger into an ever leaner part of the fuel map.

Turning in the fuel screw (the one with the locking collar) moves the fuel delivery profile forward or backward... and it's reversible.


Can you tell I personally won't be grinding on the boost pin any time soon ??!!  ;-)



Vince

[regcheeseman]

nice response mate.

Binning the nylon shim is reversible, but in my mind would be more about tuning for economy, since you are effectively lifting the plunger into an ever leaner part of the fuel map.

Not so, surely? binning the nylon shim will allow the pin to travel further thus increasing the amount of fuel?

Dialing back the star wheel inside the LDA that preloads the boost response spring will move the plunger's response curve down into the sections you've labeled "12 psi"... pushing in more fuel at lower boosts.

Quite so, and fine on a stock 7 psi motor, but if I reduce the springs preload and add the motors current 15 + psi than it's gonna be off the fuel curve way too early?

Turning in the fuel screw (the one with the locking collar) moves the fuel delivery profile forward or backward... and it's reversible.

On the NA pump I'm stripping it seems that this screw only hold the idle position or am I still barking up the wrong tree?

[Tintin]

If you can do it, more travel is better:
 

Here different pin shape, your pin are the second in the first pic,  and the last pin without diaphragm it's a machined pin on iron stem, second pic is the machined pin.